(a) Fields of the Invention
The present invention relates to optical devices which have optical chips mounted thereon and which are used for cameras such as camcorders, digital cameras, or digital still cameras and optical pickup systems for CDs, DVDs, or MDs.
(b) Description of Related Art
In recent years, optical devices have been incorporated in cameras such as camcorders, digital cameras, or digital still cameras and optical pickup systems for CDs, DVDs, or MDs. The optical devices are each provided in a package form produced in such a manner that an optical chip is mounted on a base of an insulating material and that the mounted optical chip is packaged with its main surface covered with a transparent plate.
FIG. 9 is a sectional view showing the structure of a solid-state image sensing device which is a type of conventional optical device (see Document 1 (Japanese Unexamined Patent Publication No. 2002-43554)). Referring to FIG. 9, the solid-state image sensing device includes, as main components, a base 131, a solid-state image sensing element 135, a transparent plate 136, and an adhesive layer 140. The base 131 of frame shape is made of thermosetting resin and has an opening 132 in its center portion. The solid-state image sensing element 135 is formed of, for example, a CCD and attached to the lower surface side of the base 131. The transparent plate 136 is made of glass and attached to the upper surface side of the base 131 so that the plate faces the solid-state image sensing element 135 with the opening 132 interposed therebetween. The adhesive layer 140 mechanically connects the transparent plate 136 to the base 131.
The lower surface of the base 131 is provided with wires 134 which are made of a gold plated layer and are embedded in the resin. The solid-state image sensing element 135 is attached to the lower surface of the base 131 and disposed so that a light receiving region 135a thereof is exposed in the opening 132.
The solid-state image sensing element 135 is provided with electrode pads (not shown) for sending and receiving signals between the solid-state image sensing element 135 and external equipment. At an end of each wire 134 adjacent to the opening 132, an internal terminal portion is exposed from the resin. The internal terminal portion of each wire 134 and the corresponding electrode pad of the solid-state image sensing element are electrically connected to each other with a bump (protruding electrode) 138 interposed therebetween. In addition, a solder ball 141 is annexed onto an external terminal portion of each wire 134. On the lower surface of the base 131, the solid-state image sensing element 135, the wires 134, and the bumps 138 are hermetically sealed with a sealing resin 137 provided around the solid-state image sensing element 135.
The solid-state image sensing device thus constructed is mounted on a circuit board in the state in which the transparent plate 136 is directed upward as shown in FIG. 9. A lens barrel with an optical imaging system incorporated therein is fixed onto the base 131 as shown by the broken lines in FIG. 9. The positional relation between the lens barrel and the base 131 has a defined accuracy required to fall within a predetermined error.
As mentioned above, the light receiving region 135a of the solid-state image sensing element 135 is disposed in the opening 132 when viewed from above. Through the optical imaging system incorporated in the lens barrel, light from an imaged object is condensed on the light receiving region 135a of the solid-state image sensing element 135. The condensed light is converted into electricity by the solid-state image sensing element 135.
Also, another example of the solid-state image sensing device has been known which uses a base having, unlike the base 131 shown in FIG. 9, a recess formed in its surface on which a solid-state image sensing element is mounted (for example, see Document 2 (Japanese Unexamined Patent Publication No. 2000-58805)).
Note that if a light receiving element and a light emitting element are disposed in the optical device, the light emitting element with a relatively small dimension is generally mounted above the light receiving element.
In recent years, optical devices with light receiving and light emitting elements disposed therein have also been put into practical use. In such devices, instead of the transparent plate 136, a hologram is attached onto the base 131 (to form a hologram unit).